It is known from UK Specification No. 1,543,039 to prepare polyisobutene-substituted succinic anhydride (PIB/MALA) by reacting a mixture of maleic anhydride and a polymer of isobutene with a molar deficiency of chlorine on maleic anhydride.
The mixture of polymer and maleic anhydride is suitably heated to the reaction temperature before it is contacted with the chlorine. The mixture is contacted with a molar deficiency of chlorine before a substantial amount, e.g. less than half, of the maleic anhydride has reacted. Suitably substantially none of the maleic anhydride has reacted. The rate of introduction of chlorine into the mixture may vary between wide limits but is preferably such that it equals the rate of chlorine uptake. Usually the chlorine is introduced over a period of from 0.5 to 10 hours, preferably of from 3 to 7 hours.
After the chlorination treatment it is advantageous to subject the resultant product mixture to a post-reaction or thermal treatment. This thermal treatment is suitably carried out at a temperature in the range from 140.degree. to 220.degree. C., preferably from 160.degree. to 210.degree. C. The conditions are usually such, that substantially no part of the product mixture is removed during this thermal treatment. The thermal treatment may be for from 0.1 to 20 hours but preferably from 0.5 to 10 hours. Longer periods tend to increase the formation of tarry by-products.
Using the above process a conversion of the polymer of isobutene (PIB, molecular weight 1029) of up to 90% is reached whereas the percentage of chlorine in the product is about 0.4%w. Comparing the above process with other art processed the most striking advantage of the first is that at reaction temperatures of about 200.degree. C. higher polymer conversions to lower chlorine containing products are obtained. These prior art processes are described in e.g. published Netherlands Applications No. 7412057 and No. 7313404 and in UK Specification No. 949,981.
It is known, e.g. from published Netherlands Application No. 7412057, to prepare polyisobutene-substituted succinic anhydride by reacting thermally a polymer of isobutene with maleic anhydride. From published Netherlands Application No. 7313404 it is known to prepare similar products by reacting thermally the polymer of isobutene with maleic anhydride until substantially all (i.e. at least half) of the maleic anhydride has been consumed and thereafter continuing the reaction in the presence of chlorine.
One problem often encoutered with these processes, which involve a substantial amount of thermal reaction, is that fairly high temperatures, e.g. temperatures about 220.degree. C., are required to achieve a satisfactory reaction rate and at such high temperatures an undesirable amount of tarry by-products are formed.
From UK Specification No. 949,981 it is known to prepare such products by containing a mixture of the polymer of isobutene and maleic anhydride with at least one mole of chlorine for each mole of maleic anhydride (one-stage chlorination route). Since such a process does not involve a substantial amount of thermal reaction it is possible to use a lower temperature e.g. a temperature of below 220.degree. C. However, the final product contains a fairly high amount of chlorine.
It is known e.g. from U.S. Pat. Nos. 3,960,889 and 4,000,162 to prepare alkylenepolyamine derivatives of the reaction product of a dehydrohalogenated polyalkene and maleic anhydride, which derivatives are useful detergent-dispersants in lubricating oil.
It has now surprisingly been found that at high PIB-conversion levels (up to 90%) the chlorine percentage in the product obtained from a similar process as that described in UK Specification No. 1,543,039 can further be decreased to less than 0.2%w if the PIB/MALA Product is subjected to a thermal treatment after excess MALA Has been stripped off.